For purposes of product returns and order filling, it is important to be able to sort and count products accurately and quickly. Such products, for example magazines and retail packages, have historically either been manually sorted and counted by human operators or manually scanned to read an affixed code, counted and then sorted by the human operator according to a product disposition signal provided from the product scanner according to the scanned code. One drawback experienced with these primarily manual methods for separating, counting and sorting is that total product processing time for sorting and counting is a function of each human operator's ability to accurately sort and count products and/or efficiently scan the products to obtain the affixed bar code for sorting and counting. Familiarity with the product and the signals indicating the disposition of each product also factor into the processing time. An additional drawback of the conventional manual separation, counting and sorting process is its susceptibility to error resulting from careless human operators directing products into improper bins. These drawbacks result in errors in the counting of products and delays in the sorting process thereby reducing the net product throughput of and profits for the sorting and counting operation.
The goals of all sorting and counting operations are accuracy, low cost and high throughput product processing. To achieve these goals and, in particular, combat the drawbacks associated with manual sorting and counting operations, automated machines have been provided to singulate stacks of products into a product stream, count the number of singulated products and then sort the products, according to an affixed bar code, for further processing. As is well known, there are two common orientations of bar codes, a ladder code orientation and a picket code orientation. These two orientations are easily distinguished from each other; a ladder code is comprised of a plurality of horizontal bars (like the rungs of a ladder) parallel to a top or bottom edge of a product, and a picket orientation is comprised of a plurality of vertical bars (like the pickets in a fence) parallel to a side edge of a product. Bar codes may be affixed to the product at any one of a number of locations on any outside surface.
The keys to proper counting and sorting of bar coded products are accurate scanning of the affixed bar codes and complete singulation of the product stack into a stream of individual products. Mechanical singulators, like the product singulation apparatus disclosed in commonly assigned, co-pending application for patent Ser. No. 593,783 filed Oct. 5, 1990, however, randomly fail to completely separate two or more products from each other. This failure to completely singulate the stacks of products creates a condition known as a "product multiple" occurrence wherein the non-singulated products either completely or partially overlap one another.
When overlapping products are present in a singulated product stream, the accuracy, throughput and profits of the sorting and counting operation are adversely affected. For example, one or more of the overlapping products are likely to be directed to an incorrect final disposition. Furthermore, in applications, such as returns processing, where accurate counting is imperative, two or more overlapping products are likely to be miscounted as a single product. Accordingly, there is a need for a method and apparatus for accurately detecting the presence of product overlaps in a singulated stream of coded products prior to sorting thereby providing for a more accurate sort and count of the product stream.